Initiative in Evolution - Walter Kidd

Table V.—Distribution of Cold and Warmth Spots.

By stimulation of cold or warmth spots there is shown, not only the quality and quantity of the stimulus, but the locality. When punctiform stimuli are applied to pairs of cold spots and pairs of warmth spots marked “local sign” is found. This Goldscheider showed to be higher for cold than warmth spots.

Cold Spots.		Warmth Spots
Palm	.8 mm.	Do. 2 mm.
Cheek, Chin and forehead	0.8 mm.	Do. 5.0 mm.
Upper arm	2 mm.	Do. 3 mm.
Back of hand, leg, thigh	3 mm.	Do. 4 mm.
Forearm	3 mm.	Do. 3 mm.
Back, chest, abdomen	2 mm.	Do. 5 mm.

Thus on the palm of the hand two pairs of cold spots .8 mm. apart are distinguished by this punctiform stimulation, whereas on this surface two pairs of warmth spots are only distinguished when they are 2 mm. apart on the cheek, chin or forehead and cold spots are distinguished when .8 mm. apart on the same surfaces warmth spots when 5 mm. apart.

Table VI.—Average lowest distances in millimetres on different areas of skin where two points are felt as two or minimal distances from which double sensation is obtained.

Skin Region.	Adult Man.	Boy aged Twelve.
Tip of tongue	1.1	1.1
Palmar surface of tip of finger (index)	2.3	1.7
Red surface of lip	4.5	3.9
Palmar surface of 2nd phalanx of finger	4.5	3.9
Dorsal surface of 3rd phalanx of finger	6.8	4.5
Side of tongue	9.0	6.8
Tongue 27 mm. from tip	9.0	6.8
Plantar surface of distal phalanx of great toe	11.3	6.8
Surface of palm of hand	11.3	9.0
Dorsal surface 2nd phalanx of finger	11.3	9.0
Forehead	22.6	18.0
Back of ankle	22.6	20.3
Back of hand	31.6	22.6
Forearm and leg	40.6	36.1
Dorsal surface of foot	40.6	36.1
Surface on outer border of sternum	45.1	38.8
Back of neck	54.1	36.1
Middle of back	67.1	31.6 to 40.6
Upper arm and thigh	67.1	31.6 to 40.6

Table VII.—(According to Weber’s Law.) Average differences in different regions of skin of sensation of pressure.

Forehead		1/30 to 1/40
Lips
Dorsum of tongue
Cheeks
Temple
Finger nail		1/10 to 1/20
Dorsal surface of forearm, leg, and thigh
Dorsal surface of hand
Dorsal surface of 1st and 2nd phalanges of fingers
Palmar surface of finger
Palmar surface of hand
Flexor surface of forearm
Dorsum of foot		More than 1/10
Dorsal surface of toes
Plantar surface of toes
Sole of foot
Surface of leg and thigh

Thus on the forehead differences of pressure are distinguished when they are increased by 1/30, whereas on the dorsum of the foot they have to be increased by 1/10 to be distinguished. This is carried out by impact of little balls of a light substances such as pith.

It may be remarked of these tabulated results that on the one hand they are the results of work extending over some seventy years and numerous observers, and on the other that, broadly looked at, they all tell the same story of stimuli in their incidence on the skin—those of pain, cold, warmth and touch. There is also one thread of origin running through all, and that is that the regions most exposed to the four stimuli show the highest development of specialised function and structure.